One main cause of coronary heart disease is coronary stenosis caused by arteriosclerosis. Coronary stenosis can cause significant changes in coronary blood flow and other hemodynamics, as well as lead to relative and absolute myocardial ischemia. Coronary angiography and intravascular ultrasound are the most common techniques for diagnosing coronary heart disease. X-ray angiography (hereinafter referred to as X-ray radiography) is an X-ray imaging system which combines conventional angiography and electronic computer image processing technology. By injecting a contrast agent into a blood vessel, X-ray radiography can dynamically observe, from different orientations (i.e., from different projection view angles), the shape and state of the vessel and any lesions thereof, as well as flow dynamics. X-ray radiography is generally adapted for examining large vessels of the heart, such as a coronary artery, as well as cervical and intracranial arteries, and is often used for diagnosing and observing arterial stenosis, occlusion, blood vessel development abnormality and blood supply conditions.
For interventional technologies, especially blood vessel reconstruction, X-ray radiography is generally required. However, the degree of stenosis evaluated through such images is not directly associated with blood flow supply and ischemic condition at the distal end of a blood vessel tree. Since 1995, a new index, the Fractional Flow Reserve (FFR), has been proposed for calculating coronary blood flow through a pressure measurement. FFR has become important for functionally evaluating coronary stenosis, and an important guiding tool for coronary revascularization. However, FFR measurement based on a pressure guide wire usually serves as an invasive intrusion measurement and may even cause a risk of trauma.
With advances in medical imaging technology and reconstruction technology, computational fluid mechanics, high-performance computing and other fields, numerical simulation calculation of FFR (virtual FFR) is a recent development. According to clinical tests, virtual FFR, which may be specific to the scale of each blood vessel level of the patient individual, generally has a very high capability to diagnose myocardial ischemia with high accuracy, sensitivity, specificity, positive and negative prediction values, compared with conventional methods.
At present, calculation methods for virtual FFR mainly include FFRCT based on coronary angiography CT, FFR simulation vFFR based on X-ray radiography image and FFRQCA based on the combination of quantitative coronary angiography with a TIMI (Thrombolysis In Myocardial Infarction) frame count method. Calculation precision and computation time are standards for judging which calculations methods are best for clinical popularization.